Antenna feed system



Feb. 8, 1944.

N. E. LINDENBLAD ANTENNA FEED SYS TEM Filed May 31, 1940 7'0 LOAD I I WTRA NSM/ TTERS INVENTOR. A/Ilj. L/NDENBLAD BY M5 ATTORNEY.

Patented Fgba 8,

ANTENNA FEED SYSTEM Nils n. Lindenblad, Rocky Point, N. 1%., assignor toRadio Corporation of America, a corporation of Delaware Application May31, 1940, Serial No. 338,177

12 Claims.

This invention relates to electrical transmission systems and, moreparticularly, to a system for feeding a load, such as an antenna system,simultaneously with energy from two transmitters operating at differentfrequencies.

One of the objects of the present invention is to enable twotransmitters operating at different frequencies to feed the same loadsystem simultaneously over different branch circuits in such a mannerthat there is no reaction between the transmitters over a wide range offrequencies.

A further object of the invention is to provide an arrangement forcoupling a pair of independent single-sided transmission lines to a pairof transmission lines delivering the energy from both of saidindependent lines in a phase quadrature relationship at the loadterminals.

Still a further object of the present invention is to enable twotransmitters operating at different frequencies to feed a tumstileantenna without interaction between the transmitters.

In accordance with a feature of the invention there is employed betweenone transmitter and the load circuit a transformer for converting from asingle-sided circuit to a circuit balanced with respect to ground.Across the balanced circuit is connected a half wave loop circuit withthe second transmitter connected to its midpoint. Energy from the secondtransmitter is thus introduced into the balanced or push-pul circuit ina push-push relationship. Then, in order to obtain a phase quadraturerelationship at the outactive components introduced into the lines dueto the heretofore mentioned connection between the single-sided andpush-pull circuits..

Further objects, features and advantages of the present invention willappear from the following detailed description which is accompanied by adrawing in which Figure 1 shows an embodiment of the invention, whileFigure 2 shows a modification of the form shown in Figure 1.

Referring, now, to Figure 1, there is shown a single-sidedtransmisslonline in the. form of a concentric cable having an outer sheath 5 and aninner conductor 6, and energized from transmitter A. I have also mown apairof lines adapt- 44) is equal and of opposite direction.

be seen that at the frequency for which the iunc tionship as the innerconductor 6. The other inner conductor 36 is directly connected to theend of the sheath 5 of the single-sided line from transmitter A and istherefore energized in phase opposition to the inner conductor 25. Inorder '15 to completely uncouple the last quarter wave section of thesingle transmission line 5, 6 from the remainder of the same so that oneside of the balanced circuit is not shorted, I have provided an outershell I surrounding the end of sheath 5.

The shell I is a quarter of the length of the operating wave long and isconnected to sheath 5 of the single transmission line at its end remotefrom the open end of sheath 5.' The length of the conducting path withinthe outer shell I and including the outer surface of sheath 5 is of suchlength that the point of connection of con- 1 ductor 36 is electricallyfreed from the outer conductor of the transmission line 6, 6 as far asradio frequency potentials are concerned. This eflect is due to the factthat the length of' the conducting path including the outer surface ofsheath 5 and the inner surface of shell 1 is substantially equal. to ahalf wavelength of the operating frequencyof transmitter A and thereforepresents a distinctly high impedance thereto at the point of connectionof conductor 38. Furthermore, no radiation can take place from thecurrent flowing along the outer surface of sheath 5 since the currentflowing along the inside of the outer shell 5 Thus it will tion isdesigned the balanced line will not be subiect to any unbalancingeffects from the connection to the single line. This condition is, howitever, true only when the surrounding section approximates a quarter ofthe length of the operating wave. If the frequency is changed or if theoperating frequency is widely modulated some current will leak over theedge of sheath 5 of the single transmission line,cand the push-pulloutput circuit will be unbalanced. In order to overcome this effect andmaintain perfect balance over a wide frequency band, I employ a secondquarter wave shell section l1 arranged in as an end-on relationship withand having'the same diameter as the outer shell I. Within the secondshell section I! is an inner conductor I! having the same diameter asthe outer diameter of sheath 5 of the single transmission line 5. ThoughI have referred to shells I and I1 separately for convenience indescription, it should be understood that in practice it may be foundmore convenient to form them in one continuous piece. The innerconductor [5 is connected at its inner end to the center conductor 6 ofthe single line and, also, to the center conductor 26 of one of thebalanced lines. The other end of inner conductor I5 is electricallyconnected to the end of shell II. The points of connection, and thedimensions of the parts are so chosen, that the junction is perfectlysymmetrical with respect to a center plane perpendicular to the axis ofshells 'l, I 1. With this construction it will be seen that looking fromthe push-pull line toward the junction along either conductor 26 orconductor 36, an exactly esimilar set of conditions is encountered.Therefore, for a-wide frequency band, or for frequencies varying widelyfrom the frequency for which the Junction is designed, the reactivedrain on conductor 36 due to an improper length of shell I is duplicatedby an equal drain on conductor 28 by shell portion I1.

From the foregoing description it will be seen that transmitter A feedstransmission lines 25,

35 in a push-pull relationship through a singlesided line 5.

transmitter B and having a central conductor 6' and an outer sheath 5'.It will be seen that there is in eflect a half wave loop connectedacross the adjacent ends of conductors 28 and I6. Such a half wave loopwill, of course, not adversely afiect the operation of the circuit asfar as transmitter A is concerned. The energy from transmitter B is fedto conductors 26 and 36 through exactly equivalent lengths of line andis therefore in an in-phase or "push-push" relationship.- Since it isdesired to feed the energy from both transmitters to the load in a phasequadrature relationship, a loop 3l'is placed in one of the transmissionlines. This loop has a length such that one output transmission line isa quarter of the mean operating wavelength, or an odd multiple thereof,longer than the other.

Figure 2 shows a more complicated arrangement required to eliminate thestill existing but balanced reactance of the coupling arrangement atfrequencies remote from the mean operating frequency. The constructionof each of the portions within the dotted box III is the same as shownin box III in Figure -1. a In Figure 2 each of the input and outputlines to boxes III are connected together through lines which differ inlength by an odd multiple, including unity, of a quarter of the meanoperating wavelength. Since all physical dimensions in each couplingunit are the same the reactance and resistance of'both sections isexactly the same and due to the quarter wave spacing each compensatesfor the other on each side of themean operating frequency. The theoryupon which this depends is disclosed in more detail inapatent to E. C.Cork, et al.. #2,165,96l, granted July 11; 1939. p

While I have particularly shown and described\ several modifications ofmy invention, it is to be distinctly understood that my invention is notlimited thereto but that improvements within the scope of the inventionmay be made.

I claim: 7

1. Means for supplying energy to a high frequency load simultaneously attwo different frequencies, a first and a second source of oscillations,each of said sources being adapted to supply one of said diii'erentfrequencies, a pair of transmission lines coupled to said load, meansfor applying energy from the first of said sources to said pair oftransmission lines in a push-pull relationship, means for applyingenergy from the second of said sources in an in-phase relationship, oneof said lines having a length from said a conductor of the other of saidpair of lines, an

outer shell surrounding the end portion of said single line, said shellbeing connected to said sheath at a distance equal to a quarter of themean operating wavelength from the end of said single line, and abalancing circuit including an inner conductor connected to the innerconductor of said single line and having a diameter equal to thediameter of the outer sheath of said, single line and an outer shellhaving a'diameter equal to the diameter of the first outer shell andconnected thereto, the inner conductor and outer shell of 'saidbalancing circuit being connected together at a distance equal to aquarter of the mean operating wavelength from the end of said singletransmission line, a second single transmission line having an outersheath and an inner conductor, a connection from its inner conductor toeach of said pair of lines, said connections each having a length equalto a quarter of the length of the mean operating wavelength, one of saidpair of lines being a quarter of the mean operating wavelength longerthan the other.

3. In combination, a first single transmission line having an outersheath and an inner conductor and a pair of transmission lines, aconnecsingleline, said shell being connected to said sheath at adistance equal to a quarter of the mean operating wavelength from theend of said single line, and a balancing circuit-including an innerconductor connected to the inner conductor of said single line and anouter shell connected to said first outer shell, the inner con-, ductorand outer shell of said balancing circuit being connected together at adistance equal to,

a quarter of the mean operating'wavelength from said last connections, asecond single transmission line having an outer sheath andan innerconductor, a separate'connection from its inner conductor to each ofsaid pair of lines, said separate connections each having a length equalto a quarter of the length of the mean operating wavelength, one of.said pair of lines being aquarter of the mean operating wavelengthlonger than the other. Y

4. In combination, a first single concentric line having an outer sheathand an inner conductor, a pair of concentric transmission lines eachhaving an outer sheath and an inner conductor, a connection from theinner conductor of said single line to an inner conductor of one oi saidpair 'of lines, a connection from the end of the sheath oisaid singleline to the inner conductor of the other of said pair of lines, an outershell surrounding the end of said single lines and its junction withsaid pair of lines, said shell being connected to the outer sheath ofsaid single line at a distance equal to a quarter of the mean operatingwavelength from the end of said sheath, and a balancing circuit,including an inner conductor having a diameter equal to the diameter ofthe outer sheath of said single line connected to the inner conductor ofsaid single line and an outer shell having a diameter equal to thediameter of said first outer shell and forming an extension thereof, theinner conductor and outer shell of said balancing circuit beingconnected together at a distance equal to a quarter of the meanoperating wavelength from the end adjacent the end of said single line,a second single transmission line having an outer sheath and 'an innerconductor, a pair of connections from its inner conductor to said pairof lines, said pair of connections each having a length equal to aquarter of the length of the mean operating wavelength, one of said pairof lines being a the operating wave longer than the other of saidbranches, a connection from one of said pair of lines to each of theinner conductors of said branches, a connection from the inner conductorof the other of said pair of lines to the end of the outer sheath ofeach of said branches, said connections differing in length by an oddmultiple, including unity, of a quarter of the operating wavelength, anouter shell surrounding the end ing connected to the outer sheath ofsaid length of the operating wave from the end of each branch, saidouter shell extending beyond the ends of said branches, and an innerconduc- -tor within the extending portion of said shells and connectedto the inner conductors of said t branches, each of-said outer shellsand said last mentioned innerconductors being connected together adistance-equal to a quarter of the length "of the operating wavebeyondvthe point of connection to said inner conductors, a second singleconcentric transmission line having an outer sheath and an innerconductor, a half wavelength loop connected across the end of each ofsaid first single line branches, connections from a midpoint on each ofsaid loops to said second single line, said last connections difieringin length .by an odd multiple, including unity, of a quarter wavelength;one of said pair of lines being aquarter wavelength longer than theother whereby phase quadrature output is obtained.

6; In combination, a pair of transmission lines adapted to supply energyto a load in a phase quadrature relationship, means for energizing saidtransmission lines in a push-pull relationship entirely irom afirstsource of oscillations of one frequency, and means for simultaneouslyenergizing said lines in an in-phase relationship entirely from a secondsource. of oscillations of a different frequency, one of said pair oflines being a quarter of the mean operating wavelength longer than theother.

'7. In combination, a first and a second transmission line and a pair ofconcentric trsion lines, each of said lines having an inner conductorand an outer shell, each of said first and second transmission linesbeing connected to a source of oscillations of difierent frequencies, a-

coupling circuit for energizing the inner conductors of said pair oflines in a push-pull relationship from only the source connected to saidfirst transmission line,- connections from the inner conductors of saidpair of lines to the inner conductor of said second line forsimultaneously energizing said pair of lines in. an in-phaserelationship from only the source connected to said second line.

8. In combination, a pair of transmission lines adapted to supply energyto a load in a phase quadrature relationship, means for energizing saidtransmission lines in a push-pull relationship entirely from a firstsource of oscillations, and means for simultaneously energizing saidlines in an in-phase relationship entirely from a second source ofoscillations, one of said pair of lines being a quarter of the operatingwavelength longer than the other, and means connected to one of saidpair of lines for neutralizing the undesired unbalance on said pairs dueto the reactance of said first means.

9. In combination, a pair of transmission lines and a first and a secondsingle transmissionline, each connected to a source of high frequencyenergy, a coupling circuit for energizing said pair of lines in apush-pull relationship from one of said single lines, connections fromsaid pair-of lines to the other of said single lines for simultaneouslyenergizing said pair of lines in an inphase relationship, said couplingcircuit including means for maintaining saidpair of transmission linesbalanced, .a second coupling circuit conof each branch of said singleline, said shells bebranches at a distance equal to a quarter of thenected to said one single line and said-pair of lines, a second set-ofconnections from said pair of linesto said other single line, theconnections of said second coupling circuit and said second set ofconnections diflering inlength from said first mentioned connections byan odd multiple, including unity, of a quarter of the mean operatingwavelength.

10. An arrangement as set forth in claim 7 in which a second set ofcoupling circuits and con"- nectio'ns connecting said 'singlelines andsaid equal to an odd. multiple, including unity. of one quarter or themean operating wavelength.

11. In combination, a pair of sources of alternating current energy. afirst and a second transdlicer means, connections from each or saidsources of energy to each of said transducer nections from saidtransducers to said load, the

connections from said second transducer to said load being one quarteroi. the operating wavelength longer than the corresponding connections15 from said first transducer means to said load.

12. In combination, a source of alternating current ener y. a first anda second transducer means, connectionsirom said source or ener y to eachor said transducer means, the connection from saidfirst transducer meansto said source being one quarter of the operating wavelength-longer thanthe connection from said second transducer means to said source, aload,and

connections from said transducers to said load,

the connection from said second transducer means being one quarter ofthe operating wavelength longer than the connection from said firsttransducermeans to. saidload.

mns E. insomnia.-

